1. Field of the Invention
This invention relates to making insulated conductors and, more particularly, methods of and apparatus for cooling an insulated conductor advanced along a substantially linear portion of a manufacturing line and then about a grooveless capstan at a downstream end of the substantially linear portion in a number of convolutions which may be varied to maintain the conductor exiting from the capstan at a desired temperature.
2. Technical Considerations in the Prior Art
In today's manufacture of communications transmission conductors, there is a trend toward using higher and higher line speeds, e.g., five thousand feet per minute or higher. This causes a demand for substantially increased cooling capacity because of the reduced time during which the conductor is exposed to a cooling medium. Obviously, those wishing to raise line speeds in existing manufacturing facilities to remain competetive may encounter substantial difficulties in attempting to increase the line length because of other equipment adjacent thereto as well as the costs involved in extensive modifications.
In addition to the requirement for increased cooling capacity, another problem relating to cooling presents itself with respect to capacitance monitoring of the insulation of the conductors. This is generally performed intermediate a downstream end of a substantially linear water trough, used in many insulating lines, and a capstan. Conventionally, the capstan includes a pair of spaced-grooved rollers, each of the rollers having generally five to nine grooves formed thereon.
Problems arise because coaxial capacitance measurements are affected by temperature and the temperature of the insulated conductor entering the grooved capstan may not be constant. Temperatures are a function of, for example, conductor gauge size, cooling capacity, and line speed. For example, when using the larger gauge size wires such as a 22 gauge conductor, the temperature of the insulation would be above that of the insulation of a 26 gauge wire which is advanced from the cooling trough into engagement with the capstan. As a result, the capacitance monitors in the shop must be recalibrated in accordance with the expected temperatures of the particular conductors advanced through the monitoring units. If this time consuming and expensive recalibration is not done, then false readings are indicated for the coaxial capacitance monitoring and are not discoverable until the conductors are assembled into a cable and mutual capacitance or capacitance-to-ground unbalance failures occur.
In today's more sophisticated communications systems, stringent requirements exist for the mutual capacitance between associated pairs of the conductors. In solid type insulation, capacitance can be generally, but not as reliably, controlled by controlling diameter-over-dielectric (DOD). But with cellular or dual insulation, control must be exercised over both capacitance and DOD.
In order to meet these requirements it is incumbent upon a manufacturer to be able to monitor the coaxial capacitance with accuracy and consistency. This is impossible with the presently used cooling arrangements unless the expensive recalibration procedures discussed hereinbefore are used.
Although the capacitance monitor could be placed after the grooved capstan, the temperature of the conductor may not be constant because of the limited capacity of commercially available grooved capstans. This may not be adequate to reduce the temperature of the conductor sufficiently to attain a desired temperature at which the capacitance is always measured.
It is desirable to measure the coaxial capacitance when the conductor is at a specified temperature to avoid the necessity for expensive recalibration procedures. To accomplish this requires an adjustment of cooling capacity depending on line speed changes, insulation material and thickness gauge size and wire preheat. The cooling capacity is comprised of the substantially linear water trough and the grooved capstan subjected to water jets or sprays, for example.
It is well known that the linear portion of the cooling trough need only be as long as is required to prevent deformation of the conductor insulation when the conductor is advanced into engagement with the capstan. This is generally sized in accordance with the requirements for a large gauge conductor or a conductor design having difficult cooling characteristics, e.g., conductors requiring a hot water cooling trough section. Any lengthening of the linear portion over that required to prevent deformation in order to increase cooling capacity is undesirable because of an undue amount of tension imparted to the insulated conductor, particularly to fine gauge, e.g., 26 gauge conductors.
Cooling capacity may also be increased by providing a capstan having a very large number of grooves for each of the rollers comprising the capstan. Then, in the event a smaller gauge conductor is run through the line, the conductor need only be wrapped along a portion of those grooves and thence through the exit end of the capstan because of the reduced amount of cooling required. This approach is undesirable because the conductor would have to be run transversely across the tops of the walls of the grooves comprising the capstan in order to avoid being threaded through all of the grooves. This may cause damage to the insulation. In the alternative, a sheave guide assembly could be used to direct the conductor from an intermediate groove. This complicates an already congested structure, may be difficult to maintain freely rotatable and still leaves an undesirable amount of string-up when using all the grooves.
Grooveless capstans have been used in the textile industry for a variety of reasons. Stringing up a fibrous material particularly of the finer denier sizes in a grooved roller or capstan is extremely time consuming. Also, the walls of the grooves may have a deleterious effect on the filamentary and fibrous material.
Grooveless capstans comprising spaced rollers, one being canted to the other have also been used in the textile industry. These are canted so as to be in non-parallel planes transverse of the axis of advance. This results in a plurality of convolutions of increasing or decreasing size which principle is used to compensate for the shrinkage or stretching in the fibers. A tapered capstan has also been used for this purpose. See, for example, U.S. Pat. Nos. 2,155,324, 2,757,101 and 2,746,281.